Release the CRC library

This implementation can advantage of hardware acceleration available
on common CPUs when using GCC and Clang. A future update may enable
this on MSVC as well.

PiperOrigin-RevId: 487327024
Change-Id: I99a8f1bcbdf25297e776537e23bd0a902e0818a1

1 files changed, 59 insertions, 0 deletions

diff --git a/absl/crc/internal/cpu_detect.h b/absl/crc/internal/cpu_detect.h
new file mode 100644
index 00000000..54cb328a
--- /dev/null
+++ b/absl/crc/internal/cpu_detect.h
@@ -0,0 +1,59 @@
+// Copyright 2022 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_CRC_INTERNAL_CPU_DETECT_H_
+#define ABSL_CRC_INTERNAL_CPU_DETECT_H_
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace crc_internal {
+
+// Enumeration of architectures that we have special-case tuning parameters for.
+// This set may change over time.
+enum class CpuType {
+  kUnknown,
+  kIntelHaswell,
+  kAmdRome,
+  kAmdNaples,
+  kAmdMilan,
+  kIntelCascadelakeXeon,
+  kIntelSkylakeXeon,
+  kIntelBroadwell,
+  kIntelSkylake,
+  kIntelIvybridge,
+  kIntelSandybridge,
+  kIntelWestmere,
+  kArmNeoverseN1,
+};
+
+// Returns the type of host CPU this code is running on.  Returns kUnknown if
+// the host CPU is of unknown type, or if detection otherwise fails.
+CpuType GetCpuType();
+
+#if defined(__aarch64__)
+// Returns whether the host CPU supports the CPU features needed for our
+// accelerated implementations. The CpuTypes enumerated above apart from
+// kUnknown support the required features. On unknown CPUs, we can use
+// this to see if it's safe to use hardware acceleration, though without any
+// tuning.
+bool SupportsArmCRC32PMULL();
+#endif
+
+}  // namespace crc_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_CRC_INTERNAL_CPU_DETECT_H_